In long horizontal wells, the production rate at the heel is often higher than that at the toe. The resulting imbalanced production profile may cause early water or gas breakthrough into the wellbore. Once coning occurs, well production may severely decrease due to limited flow contribution from the toe. To eliminate this imbalance, inflow control devices (ICDs) are placed in each screen joint to balance the production influx profile across the entire lateral length and to compensate for permeability variations.
By restraining, or normalizing, flow through high flow rate sections, ICDs create higher drawdown pressures and thus higher flow rates along the borehole sections that are more resistant to flow. This corrects uneven flow caused by the heel-toe effect and heterogeneous permeability.
Although they are called inflow control devices, ICDs are also used to manage fluid outflow in injection wells. In some cases, modeling reveals that it is more effective to place ICDs in the injector well than in the producer. In many cases, installing the devices in both the injector and producer wells may be the best option.
Stalder investigated the flow distribution control of ICDs. Based on the observation of an ICD-deployed SAGD well pair in a Surmont SAGD operation, he came to the conclusion that an ICD -deployed single tubing completion achieved similar or better steam conformance as compared to the standard toe/heel tubing injection. In addition, the ICD completion significantly reduced tubing size, which in turn reduced the size of slotted liner, intermediate casing, and surface casing. The smaller wellbore size increased directional drilling flexibility and reduced drag making it easier and lower cost to drill the wells. Thus, wells can be drilled much longer than current SAGD wells, which tend to be between 500 and 1000 m.
Indeed, ICDs have been installed in hundreds of wells during the last decade, being now considered to be a mature, well completion technology. Steady-state performance of ICDs can be analyzed in detail with well modeling software. Most reservoir simulators include basic functionality for ICD modeling.
Currently, there are four primary types of passive ICD designs in the industry: nozzle-based (restrictive) (FIG. 1), helical channel (frictional) (FIG. 2), tube-type (combination of restrictive and friction) (FIG. 3) and hybrid channel (combination of restrictive, some friction and a tortuous pathway) (FIG. 4). They use four different methods to generate a pressure drop.
The nozzle-based ICD uses fluid constriction to generate an instantaneous differential pressure across the device by forcing the fluid from a larger area down through small diameter port, creating a flow resistance. The benefits of nozzle-based ICD are its simplified design and easier nozzle adjustment immediately before deployment in a well should real-time data indicate the need to change flow resistance. The disadvantage of nozzles are the small diameter ports required to create flow resistance, which also make them prone to both erosion from high-velocity fluid-borne particles during production, and susceptible to plugging, especially during any period where mud flow back occurs.
The helical channel ICD uses surface friction to generate a differential pressure across the device. The helical channel design is one or more flow channels that wrapped around the base pipe. This design provides for a distributed pressure drop over a relatively long area, versus the instantaneous loss using a nozzle. Because the larger cross-sectional flow area of the helical channel ICD generates significantly lower fluid velocity than the nozzles of a nozzle-based ICD with a same FRR, the helical channel ICD is more resistance to erosion from fluid-borne particles and resistant to plugging during mud flow back operations. The disadvantage of helical-channel ICD is its flow resistance is more viscosity-dependent than the nozzle-based ICD, thus start up is delayed. The cost of delayed production has been estimated at $2M/month (the figure assumes no production for a month). The viscosity dependence could also allow preferential water flow should premature water breakthrough occur. Also, the helix ICD is not adjustable.
The tube-type ICD design incorporates a series of tubes. The primary pressure drop mechanism is restrictive, but in long tubes. This method essentially forces the fluid from a larger area down through the long tubes, creating a flow resistance. Because of the additional friction resistance, the larger cross-sectional flow area of the tube-type ICD generates lower fluid velocity than the nozzles of a nozzle-based ICD with a same FRR, the tube-type ICD is more resistance to erosion from fluid-borne particles and resistant to plugging during mud flow back operations. However, since the friction resistance is much less than the local resistance, the tube-type ICD is less viscosity-dependent than the helical channel ICD with a same FRR.
The hybrid ICD design incorporates a series of flow slots in a maze pattern. Its primary pressure drop mechanism is restrictive, but in a distributive configuration. A series of bulkheads are incorporated in the design, each of which has one or more flow cuts at an even angular spacing. Each set of flow slots are staggered with the next set of slots with a phase angle thus the flow must turn after passing through each set of slots. This prevents any jetting effect on the flow path of the downstream set of slots, which may induce turbulence. As the production flow passes each successive chamber that is formed by bulkheads, a pressure drop is incurred. Pressure is reduced sequentially as the flow passes through each section of the ICD. Without the need to generate the pressure drop instantaneously, the flow areas through the slots are relatively large when compared to the nozzle design of same FRR, thus dramatically reducing erosion and plugging potential.
In addition to these basic flow patterns and pressure drop mechanisms, the commercially available ICDs include other desirable features, such as sand screens. See e.g., the Equalizer and the Equalizer Select, both from Baker Hughes (FIG. 5). The Equalizer uses a helical flow-type design, whereas the Equalizer Select, in contrast, uses a hybrid type design that incorporates a series of flow chambers, each containing a restriction. As the production flows through each successive chamber, pressure is reduced sequentially. Each set of flow slots is staggered, so flow must turn after passing through each chamber, and this configuration minimizes jetting effects. Flow area through the slots is larger than openings in analogous orifice ICDs, so the potential for plugging and erosion is dramatically reduced. Furthermore, this device is adjustable by rotating the overlying tube or sleeve so as to open or close the various channels. As used herein, this specific pattern of a plurality of different length flow pathways, each having large flow chambers with staggered slots and an adjustable sleeve to control which length flow pathway is used is known as the “select” pattern, and it is a variation on a hybrid pattern.
Recently a new type of ICD called an autonomous ICD or AICD was developed. See US20140209297. In this ICD, the flow is vortex shaped, with shortcuts to the center (FIG. 7). The vortex has two intake on separate sides and a port to the inner tube in the center. Oil, which is thicker, takes the shorter route via the shortcuts and thus experiences less pressure drop and a faster rate of production. Water, which is much thinner, takes the longer route, spiraling all the way to the center, with much greater pressure drop and thus less water is produced.
Although all ICD's offer benefit, the reality is that none of these ICDs alone meets the ideal requirements of an ICD designed for the life of the well: high resistance to plugging and erosion, high viscosity insensitivity, and yet at the same time allows for flow control of the more complex flow profiles from enhanced oil recovery methods, such as SAGD where oil viscosity is higher during startup, where temperatures have not yet reached a high, and viscosity reduces as the temperature increases. Therefore, the selection and optimization of ICDs for specific reservoirs, especially heavy oil reservoirs, is still needed in the art.